Generally, a vehicle equipped with a sliding door is provided with a power supply device for supplying electric power from a vehicle body to a sliding door (for example, refer to Patent Literature 1). That is, a battery or the like mounted on the vehicle body and electrical components provided on the sliding door are electrically connected by a wire harness of the power supply device so that electric power is supplied. One end of the wire harness of such a power supply device is swingably supported by a vehicle-body-side protector and the other end is swingably supported by a sliding-door-side protector.